Overall objectives: Primarily to develop immunizing agents to produce protective immunity against filarial infections and secondarily to investigate the mechanisms of protective immunity or acquired resistance in filariasis. Current Goals: (1) To determine the immunogenicity of irradiated larval vaccines against Brugia pahangi infections in jirds (Kr30) and dogs (Kr2.25); (2) to evaluate the immunogenic capacity of microfilarial and ES (excretory-secretory products) vaccines against B. pahangi infections in jirds; (3) to characterize the parasitological, pathological and immunological developments of B. pahangi infections in jirds, hamsters, and dogs, relative to the route of inoculation; (4) to determine the immunologic role of 4th stage larvae of B. pahangi surgically transferred to the peritoneal cavity of jirds and hamsters; (5) to determine the effects of selective immunosuppressive measures (whole body irradiation) and agents (heterologous antithymocyte serum and Cyclophosphamide) on the immune response of jirds and dogs infected with B. pahangi; (6) to characterize delayed hypersensitivity (DH) reactions in B. pahangi-infected or -sensitized jirds and dogs, using various specific filarial antigenic preparations, in order to determine the role of cell mediated immunity in acquired resistance; (7) to characterize immediate hypersensitivity and arthus reactions in jirds and dogs infected with B. pahangi; (8) to investigate the migratory behavior and distribution of B. pahangi filariae and resulting pathology in dogs, and (9) to determine the degree of acquired resistance in jirds to B. pahangi by superinfection.